1. Field of the Invention
The present invention relates to spring brake actuators used on commercial trucks, and more particularly to an apparatus and method for attaching either the outer spring brake housing, the outer service brake housing, or both, of a spring brake actuator to a central adaptor made of the same or a dissimilar metal.
2. Description of the Prior Art
Various forms of pneumatic vehicle spring brake actuators have been introduced over the years primarily for use in the trucking industry. A typical actuator includes a service brake portion which is used for slowing or stopping a vehicle, and may also include an emergency or parking brake portion. The service brake portion is characterized by a closed housing which contains a movable diaphragm stretched across the inside. One side of the diaphragm is connected to a centrally located slidable push rod which extends out of the housing for attachment to the brakes of the vehicle. On the other side of the diaphragm a sealed chamber is formed within the housing.
An opening is provided in the sealed chamber for connection to a pneumatic (air) pressure source usually provided by an on-board air compressor. The brakes of the vehicle can be applied by introducing sufficient pneumatic pressure into the sealed chamber to act against the service brake diaphragm which moves the push rod out. A small return spring is provided inside the housing around the push rod to urge it to retract when the air pressure behind the diaphragm is reduced.
When employed, a typical emergency brake portion is attached directly behind or made a part of the service brake assembly. The emergency brake is a separate closed housing which contains a heavy compression spring and a second movable diaphragm in sealed contact with a slidable central rod which communicates directly with the push rod of the service brake.
A second sealed chamber is formed inside the emergency brake housing on one side of the diaphragm, and the heavy compression spring is deployed on the opposite side. As with the service brake, the sealed chamber of the emergency brake is connected to the on-board pneumatic source of the vehicle. As long as sufficient air pressure is provided, the diaphragm in the emergency brake will remain fully extended thereby compressing the large spring. However, should pressure fall, or should there be a leak in the sealed chamber, the diaphragm will be unable to hold the large compression spring in place. When this occurs, either slowly or quickly, the large compression spring will cause the push rod to extend out thereby applying the brakes of the vehicle.
Under normal conditions, when the vehicle is parked, the air pressure to the emergency brake portion is cut off causing the large compression spring to apply the brakes.
Because the spring brake assembly is a critical safety system, it has to be designed and manufactured for exceptional reliability. Moreover, because the compression spring inside the spring actuator must exert a sufficient force to apply a maximum braking force to the vehicle independent of any external air pressure assistance from the service brake system, the spring in its compressed state stores sufficient kinetic energy to be lethal if the spring brake housing is opened without first taking adequate precautions to secure the spring in its compressed state or to release the stored energy in a controlled manner.
It is conventional to fabricate the spring brake housing containing the compression spring and diaphragm in two opposing sections (an aluminum adaptor housing, and a steel cap or cup) separated by the periphery of the diaphragm, with the two opposing sections being clamped together with sufficient force to maintain an air-tight seal between the diaphragm and the housing. Since unauthorized opening of the housing is potentially dangerous to the inexperienced mechanic, and since unauthorized re-sealing using defective seals or improper procedures could result in a poor diaphragm seal or other internal defect, it is also conventional to discourage unauthorized access, disassembly, and reassembly of the housing by appending a warning label to the housing and using a clamping means which is temper-resistant or at least tamper-evident, so that a new clamping means, not readily available to unauthorized personnel, is required before the housing can be reassembled.
Because of the danger presented by the compression of the large spring of these brake systems, numerous inventions have been patented which provide different ways of improving safety. Many of these inventions are directed towards securing the assembly of the two halves of the housing between which the diaphragm is deployed.
A typical service brake actuator housing is made of two steel cups which form the two halves. When combined with an emergency brake actuator, the housing has three distinct parts: a lower cup which forms the bottom of the service brake actuator, an upper cup which forms the top of the emergency brake actuator, and an hourglass-shaped central body or adaptor which is provided between them. The adaptor makes up the top half of the service brake housing, and the bottom half of the emergency brake housing. Normal positioning of the two brake diaphragms results in the adaptor being part of the sealed chambers of both the service brake and the emergency brake. As a result, it is common for the adaptor to include the openings into each chamber for attachment to the pneumatic pressure source for the brakes.
The below-listed United States and foreign patents are known to exist:
______________________________________ No. Patent No. Date Inventor ______________________________________ 1 2,541,205 February 13, 1951 Christophersen 2 3,101,133 August 20, 1963 House 3 7308049.6 1973 Bosch (German) 4 028074 June 27, 1978 Girling (G.B.) 5 4,850,263 July 25, 1989 Rumsey 6 4,960,036 October 2, 1990 Gummer 7 5,062,455 November 5, 1991 Schurter 8 5,067,391 November 26, 1991 Choinski 9 5,193,432 March 16, 1993 Smith 10 5,205,205 April 27, 1993 Choinski 11 5,285,716 February 15, 1994 Thompson 12 5,315,918 May 31, 1994 Pierce 13 5,353,688 October 11, 1994 Pierce ______________________________________
These patents disclose different methods and apparatus for attachment of the two halves or cups of a brake housing. Annular clamps are taught in U.S. Pat. Nos. 2,541,205 to Christophersen; 4,960,036 to Gummer, et al; and 5,193,432 to Smith. Such clamps are bulky and cumbersome in that the flanges, nuts and bolts used for connection may not easily fit into the cramped brake area of a vehicle.
Various ways of crimping or bending the edge flanges of the two housing cups are taught in U.S. Pat. No. 3,101,133 to House; a German Patent Application No. G 73 08 049.6 filed by Bosch; and U.S. Pat. No. 4,850,263 to Rumsey. The Rumsey patent utilizes overlapping lips where one is spinned over the other and bent into position by use of the lathe or other suitable machine. Each of these devices is limited to the use of a strong bendable metal such as steel.
The three U.S. Patents to Gummer and Choinski (U.S. Pat. Nos. 4,960,036; 5,067,391; and 5,205,205) each disclose use of a clamp ring, use of a metal spun annular crimp of a flange on one of the housing cups, and the use of a separate circular channel clamp for attachment of the housing cups. Clamp rings are bulky and dangerous as noted above; and, although the circular channel clamp is a more permanent structure, it, as well as the metal spun flanges, are again limited to use with steel.
The use of a snap ring for attachment is shown in U.S. Pat. No. 5,353,688 to Pierce, et al, and in U.K. Patent No. GB 2,000,225A to Girling Midland, etc. U.S. Pat. No. 5,315,918 to Pierce discloses several methods of attachment including bayonet, screw thread, slots plus pins, and welds. Each of these methods of attachment requires that the cup and/or adaptor be uniquely modified in order to hold or accept such things as the snap ring, the pins, the screw threads, the slots, etc. Such adaptations render the cup and adaptor parts unusable except with correspondingly adapted parts, thereby severely limiting overall use, especially for repair and reuse.
The welding together of two halves of like material is shown in U.S. Pat. Nos. 5,062,455 to Schurter and U.S. Pat. No. 5,285,716 to Thompson.
It is desirable to be able to use central adaptor parts in brake actuators that are cast from aluminum as opposed to die pressed from steel sheets. However, attaching such dissimilar metals together has heretofore only been accomplished by use of annular clamps or the like. The ears, nuts and bolts of such clamps create significant clearance problems in the close tolerances of the brake area of a vehicle, making such methods of attachment unattractive.
Because of its hourglass shape, making an adaptor from steel requires the welding together of two halves. There is great expense involved in creating the necessary tooling to make these two halves, and then attaching them together. However, the price of aluminum can make it an attractive alternative to steel as a material to make the adaptor from.
It is also desirable for a brake manufacturer or remanufacturer to be able to use its conventional existing aluminum molds, or its existing steel tooling for that matter, to create adaptor pieces that may be more securely attached to the housing cups. Thus, it is equally desirable to have a secure attachment device that does not require retooling of the parts that are to be attached together.
Casting the adaptor pieces from aluminum is also desirable in that, compared to steel, many different molds may be easily and cheaply created for the various sized pieces.
In order to avoid increasing labor and service costs, it is common for a brake actuator having a single worn out component (e.g. a diaphragm) to simply be replaced in its entirety by another brake actuator, as opposed to repairing the actuator or replacing the worn out part in the field. When this occurs, the remaining parts of the old brake actuator, particularly the housing cups and adaptor, should be reusable for remanufacturing. It is therefore desirable to have a secure attachment method and device for the adaptor and housing cups that gives the brake actuator a long useful life, yet allows the adaptor and housing cups to be disassembled without significant damage in order that they may be reused or remanufactured into brake actuators with correspondingly long useful lives.
The problem presented in using aluminum adaptors in spring brake assemblies is securely attaching them to their steel counterparts. The present invention provides such a method and apparatus, while at the same time accomplishing many of the desirable conditions described above.